Alpha-olefins can be copolymerized with rigid cyclic olefins, such as norbornene, 5-ethylidene-2-norbornene and dicyclopentadiene, using various polymerization catalysts. When these copolymers contain more than 30 wt % cyclic olefins, they are typically amorphous and transparent (>90% light transmittance) and have glass transition temperatures (Tgs) above room temperature (>50° C.). With higher levels of cyclic olefin incorporation they have exceptionally high moduli (>2900 MPa), heat distortion temperatures (>130° C.@66 psi), and Rockwell hardness (>100). However, they have very poor notched Izod impact properties (<0.5 ft-lb/in@room temperature) and have brittle failures in the instrumented impact test at room temperature and below. (Brittle failures are cracks that propagate without plastic deformation of the polymers.)
Thus, without modification, cyclic olefin copolymers (COCs) have too little impact resistance to be used in most structural applications, such as automotive components. For automotive and other structural applications the ideal materials would have good impact properties and good heat distortion temperatures, while maintaining as high as possible flexural, tensile, and Young's moduli.
To improve their impact resistance, cyclic olefin copolymers are therefore generally blended with various elastomers. A number of blends of these types of materials are known in the art. U.S. Pat. No. 4,918,133, for example, discloses a cycloolefin type random copolymer composition, which is alleged to exhibit excellent heat resistance, chemical resistance, rigidity, and impact resistance, and which is a blend of several types of copolymer materials. The copolymer compositions of the '133 patent comprise (A) a random copolymer containing an ethylene component and a cycloolefin component and having certain intrinsic viscosity characteristics and a softening temperature (TMA) of not lower than 70° C., and (B) one or more non-rigid copolymers. The blends are prepared by solution blending and co-precipitation of the two blend components, by dry-blending, or by melt-mixing.
The cycloolefin component of the copolymer (A) in such compositions of the '133 patent can be any of a large number of 1- to 4-ring bridged cyclic olefins having a single double bond, such as bicyclo[2,2,1]hept-2-ene (norbornene) and tricyclo[4,3,0,12.5]-3-decene, among many others. The non-rigid copolymer (B) can be selected from: (i) a random copolymer containing an ethylene component, at least one other α-olefin component and a cycloolefin component and having certain intrinsic viscosity characteristics and a softening temperature (TMA) of below 70° C., (ii) a non-crystalline to low crystalline α-olefin type elastomeric copolymer formed from at least two α-olefins, (iii) an α-olefin-diene type elastomeric copolymer formed from at least two α-olefins and at least one non-conjugated diene, and/or (iv) an aromatic vinyl type hydrocarbon-conjugated diene copolymer or a hydrogenated product thereof.
Similarly, U.S. Pat. No. 4,992,511 also discloses cyclo-olefinic random copolymer compositions which are alleged to exhibit excellent heat resistance, heat aging resistance, chemical resistance, weather resistance, solvent resistance, dielectric properties, rigidity, impact strength and moldability, and which comprise blends of several types of copolymer materials. These compositions comprise (A) a similar type of cyclo-olefinic random copolymers as are disclosed in the '133 patent, which copolymers contain an ethylene component and a cyclo-olefinic component (which can be a cyclic diene); (B) at least one flexible polymer having a glass transition temperature (Tg) of not more than 0° C.; and (C) an organic peroxide to promote cross-linking of the polymeric components. The blends may be prepared by solution blending and co-precipitation of the two blend components or by melt-mixing.
The flexible polymer component of the '511 compositions can be selected from (a) flexible cyclo-olefinic random copolymers comprising an ethylene component, a cyclo-olefin component which can include cyclic dienes, and an alpha-olefin component having 3 to 20 carbon atoms; (b) amorphous or low-crystalline flexible olefinic copolymers comprising at least two components selected from an ethylene component and alpha-olefin components having 3 to 20 carbon atoms; (c) flexible olefin/nonconjugated diene copolymers comprising a nonconjugated diene component and at least two components selected from an ethylene component and alpha-olefin components having 3 to 20 carbon atoms, and (d) flexible aromatic vinyl copolymers selected from random copolymers and block copolymers each comprising an aromatic vinyl hydrocarbon component and a conjugated diene component, and hydrogenation products of these copolymers. No hydrogenation of the pendant olefin units in the cyclo-olefinic random copolymer or elastomeric copolymer compositions is disclosed as part of the blend preparation process.
European Patent Application No. 0 726 291 A1 discloses cycloolefin resin compositions comprising an ethylene/cycloolefin random copolymer and an aromatic vinyl/conjugated diene block copolymer or hydrogenation product thereof. These compositions may be prepared by solution blending followed by solvent evaporation or co-precipitation of the two blend components, or by melt-kneading. No hydrogenation of the pendant olefin units in the cycloolefinic random copolymer or elastomeric copolymer compositions is disclosed as part of the blend preparation process.
Additional references of interest involving COC/elastomer blends include: EP 0 566 988 B1; EP 0 597 119 B1; EP 0 608 903 B1; EP 0 647 676 B1; U.S. Pat. Nos. 5,087,677; 5,359,001; 5,574,100; 5,753,755; 5,854,349; 5,863,986; 6,090,888; 6,225,407; 6,255,396; 6,342,549; 6,590,033; 6,596,810; 6,696,524; US 2003/0096898; US 2003/0125464; US 2004/0236024; US 2005/0014898; JP 05320267; JP 05320268; JP 07247386; JP 07292181; JP 10095881; JP 03255145; JP 01318054; JP 03079611; JP 04170453; JP 04170454; JP 05009351 and JP 2004/156048.
As illustrated by the preceding discussion of representative prior art, much of the previous work involving cyclic olefin copolymer compositions has focused on copolymers of norbornene and other cyclic olefinic comonomers having a single double bond. Cyclic dienes such as dicyclopentadiene (DCPD) have also been used. DCPD is a cyclic olefin comonomer of particular interest because of its low cost and ready availability. The cyclic olefin DCPD comprises two double bonds. Thus, copolymers of DCPD with ethylene or other α-olefins, which copolymers can include terpolymers of DCPD with ethylene and other α-olefins and/or other cyclic olefin termonomers (herein all collectively encompassed by the term “DCPD-based copolymers”), retain a residual double bond in the cyclic olefin moiety after copolymerization.
The presence of residual unsaturation within DCPD-based copolymers can render such copolymers relatively unstable. For example, residual double bonds in ethylene-dicyclopentadiene (E/DCPD) copolymers make these materials susceptible to crosslinking, oxidation and other unwanted side reactions during processing and use. Similar problems can arise if the elastomer utilized in combination with E/DCPD in such copolymer compositions to modify the impact properties thereof also contains any residual unsaturation due to the nature of the comonomers used therein. Thus, if economically attractive DCPD-based materials are to be used as the basis for structural polyolefin preparation, the residual unsaturation within such copolymers needs to be eliminated or reduced by means of partial or complete hydrogenation or other derivatization of the residual double bonds within such copolymer structures.
One approach to preparing stabilized DCPD-based cyclic olefin copolymers for structural uses involves the use of partially hydrogenated DCPD as a comonomer for copolymerization in place of DCPD itself. In partially hydrogenated DCPD (hereinafter referred to as HDCPD), the DCPD cyclopentenyl olefin (which becomes a pendant sidechain olefin after copolymerization in regular DCPD) is selectively saturated, whereas the DCPD norbornenyl olefin (the copolymerizing unit) is retained. This strategy is undesirable because of the relatively higher cost of HDCPD arising from the additional preparation step, difficulties of selective hydrogenation (e.g., separation of HDCPD from DCPD, fully saturated DCPD, and isomers), and the necessity of repurifying the HDCPD monomer to levels acceptible for metallocene polymerization processes. Thus, it is advantageous to eliminate the residual olefins in DCPD-based cyclic olefin copolymers by copolymerizing DCPD itself with ethylene and/or an alpha-olefin or termonomer, and then subsequently hydrogenating the residual olefins in the product polymer. This also adds an extra (yet less costly) step to the preparation of the cyclic olefin copolymer. It is thus additionally desirable to find ways to minimize the cost and difficulty of this hydrogenation step, such as by combining the hydrogenation step with other process steps used to prepare the final material containing the at least partially hydrogenated DCPD-based cyclic olefin.
Another potential obstacle in preparing structural polyolefin materials based on DCPD-containing copolymers combined with impact resistance-enhancing elastomers involves problems which can arise when these two types of materials are blended. Blending of cyclic olefin-based, e.g., DCPD-based, copolymers with elastomers is commonly achieved by melt-mixing these two polymer types followed by extrusion. However, the high Tgs of the DCPD-based cyclic olefin copolymer base materials (up to 160° C.) can require that melt-mixing and extrusion be carried out at high temperatures (>230° C.). Thus to avoid degradation of both the base copolymer and the elastomer used as the impact modifier, it is necessary to minimize both the time and temperature of melt-mixing, yet still provide conditions that ensure good mixing between the base material and the elastomer.
Given the foregoing considerations, there is continuing interest in developing procedures for producing, using economically attractive components, polymer mixtures which can be fashioned into structural polyolefin materials that have a desirable combination of thermal and structural property characteristics, including impact resistance. Such procedures involve those which render the resulting mixture of polymers partially, and or even completely, free of moieties such as unsaturation which can adversely affect the chemical stability of such materials either during their preparation or during their end use. Such preparation procedures also are those which avoid or minimize the need for techniques such as melt-mixing that must be carried out under temperature conditions which can degrade the polymers being processed, and furthermore minimize the complexity and cost associated with polymerization and blending. The advantageous properties of such polymer mixtures can thereby be preserved.